AllMetanitLessons/OpenCode/_4th.java - master - GermanezZ/JavaExercises

AllMetanitLessons/OpenCode/_4th.java
139 строк4 KB
germa
Уроки по Metanit
04 дек 2024, 20:39
04 дек 2024, 20:3948d575a
package AllMetanitLessons.OpenCode;

import java.util.Scanner;
import java.util.Stack;

/*Прочитать с экрана консоли математическое выражение, которое содержит цифры, знаки +,-,*,/.
Вычислить выражение с учетом приоритета операций. К примеру введено 10+3*7. Ответ 31.*/
public class _4th {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);
        String expression = in.nextLine();

        System.out.println(new Calculator().decide(expression));


    }

}




class Calculator{
    public double decide(String expression){
        String prepared = preparingExpression(expression);
        String rpn = ExpressionToRPN(prepared);
        return rpnToAnswer(rpn);
    }

    private String preparingExpression(String expression){

        String preparedExpression = new String();
        for (int token = 0; token < expression.length(); token++){
            char symbol = expression.charAt(token);

            if (symbol == '-'){
                if (token == 0)
                    preparedExpression += '0';
                else if (expression.charAt(token-1) == '(')
                    preparedExpression+='0';
            }
            preparedExpression+=symbol;
        }

        return preparedExpression;
    }

    private String ExpressionToRPN(String Expr){

        String current = "";
        Stack<Character> stack =  new Stack<>();

        int priority;
        for (int i = 0; i< Expr.length();i++){
            priority = getPriority(Expr.charAt(i));

            if (priority == 0)
                current += Expr.charAt(i);

            if (priority == 1)
                stack.push(Expr.charAt(i));

            if (priority > 1){
                current+=' ';
                while (!stack.empty()){
                    if (getPriority(stack.peek()) >= priority) {
                        current += stack.pop();
                    }
                    else break;
                }
                stack.push(Expr.charAt(i));
            }

            if (priority == -1){
                current+=' ';
                while (getPriority(stack.peek()) != 1) {
                    current += stack.pop();
                }
                stack.pop();
            }
        }

        while (!stack.isEmpty()) {
            current += stack.pop();
        }
        return current;
    }

    private double rpnToAnswer(String rpn){

        String operand;
        Stack<Double> stack =  new Stack<>();

        for (int i = 0; i< rpn.length(); i++){
            if (rpn.charAt(i) == ' ' )
                continue;
            if (getPriority(rpn.charAt(i)) == 0){
                operand = new String();
                while (rpn.charAt(i) != ' ' && getPriority(rpn.charAt(i)) == 0) {
                    operand += rpn.charAt(i++);
                    if (i == rpn.length())
                        break;
                }
                    stack.push(Double.parseDouble(operand));
                }

                if(getPriority(rpn.charAt(i)) > 1){
                    double a = stack.pop(), b = stack.pop();

                    if (rpn.charAt(i) == '+') stack.push(b+a);
                    if (rpn.charAt(i) == '-') stack.push(b-a);
                    if (rpn.charAt(i) == '*') stack.push(b*a);
                    if (rpn.charAt(i) == '/') stack.push(b/a);
                }
            }

        return stack.pop();
        }




    private int getPriority(char token){
        if (token == '*' || token == '/')
            return 3;
        else if(token == '+' || token == '-')
            return 2;
        else if(token == '(' )
            return 1;
        else if(token == ')' )
            return -1;
        else
            return 0;
    }


}